1. Field of the Invention
This invention relates to positive battery electrodes composed of sodium cobalt dioxide. More particularly, this invention relates to such electrodes in which the cobalt dioxide is in the P2 phase and to batteries comprising such electrodes.
2. Prior Art
The use of elastomeric binders for cathodes are known. For example, S P.S. Yen, et al., "Elastomeric Binders for Electrodes", J. Electrochem. Soc., 130p. 1107 (1983) describes the use of ethylene propylene diene terpolymer as a binder for cathodes. In particular, cathodes for which elastomers are useful as binders are finely divided alkali metal intercalation compounds. Examples of intercalation compounds are found in European Patent No. 0070107 Al; MurPhy et al., J. Electrochem. Soc., 126, 349 (1979) and Murphy et al., Mat. Res. Bull., 13, 1395 (1978) which disclose batteries based on lithium intercalation in layered dichalcogenides.
Negative electrodes for non-aqueous batteries composed of alkali metal alloys are known. For example, U.S. Pat. No. 4,002,492 discloses electrochemical cells having an anode consisting essentially of lithium aluminum that contain lithium in amounts between about 63 and 92 percent by weight and the balance essentially aluminum. Anodes composed of lithium and aluminum are also disclosed in Rao et al., J. Electrochem. Soc., 124, 1490 (1977), and Besenhard, J. Electroanal. Chem., 94. 77 (1978). Negative electrodes containing alloys of sodium are disclosed in U.S. Pat. No. 4,668,596 of Shacklette et al. and U.S. Pat. No. 4,753,858 of Jow.
Conjugated backbone polymers, e.g., polyacetylene, polyphenylene, polyacenes, polythiophene, poly(phenylene vinylene), poly(furylene vinylene), poly(thienylene vinylene), polyazulene, poly(phenylene sulfide), poly(phenylene oxide), polythianthrene, poly(phenylquinoline), polyaniline, polythiophene, and polypyrrole, have been suggested for use in a variety of applications based upon their characteristic of becoming conductive when oxidized or reduced either chemically or electrochemically. The secondary battery application described by, e.g., MacDiarmid et al. in U.S. Pat. No. 4,321,114 (1981); J. de Physique Colloque C3, Vol. 44 (1983), articles beginning on page 579, page 615 and page 537; and K. Kaneto et al., Japanese J. of Applied Physics, Vol. 22, pp. L567-L568 (September 1983) and pp. L412-L414 (July 1983), employs one or more electrodes having conjugated backbone polymers as the electroactive material. Such electrodes can, for example, be reversibly complexed with alkali metal or tetraalkylammonium cations during battery cycling, most commonly with insertion of cations into a polymer anode (the negative battery electrode) occurring during charging The more such cations are inserted, the more conductive the electrode becomes and the more cathodic the potential of the anode becomes.
Various studies have been made on sodium cobalt dioxide and the electrochemical intercalation of sodium. Illustrative of these studies are those described in J. Molenda et al., "Transport Properties of Na.sub.x CoO.sub.2-y ", Solid State Ionics, 12 pp. 473-477 (1984); Claude Fouassier et al. "Sur de Nouveaux Bronzes Oxygenes de Formule Na.sub.x CoO.sub.2 (x-1). Le Systeme Cobalt-Oxygene-Sodium", Journal of Solid State Chemistry, 6, pp. 532-537 (1973); S. Kikkawa et al., "Electrochemical Aspects of the Deintercalation of Layered AMO.sub.2 Compounds", Journal of Power Sources, 14, pp. 231-234 (1985); Claude Delmar et al. "Electrochemical Intercalation of Sodium in Na.sub.x CoO.sub.2 Bronzes", Solid State Ionics, 3/4, pp. 165-169 (1981); and Jean-Jacques Braconnier et al., "Comportement Electrochemique Des Phases Na.sub.x CoO.sub.2 ", Mat. Res. Bull., 15, pp. 1797-1804 (1980).
Composite structures of a conjugated backbone polymer and a non-electroactive material have been described in U.S. Pat. No. 4,294,304 and in the above J. de Physique issue, articles beginning on page 137 and on page 151. Representative other components that have been blended with polyacetylene or onto which polyacetylene or polypyrrole have been deposited include polyethylene, polystyrene, graphite, carbon black, NESA glass and silicon In selected instances, such composite structures have been suggested for use in batteries, see Showa Denko K. K., European published Patent Application No. 76,119 (1982).
Each of U.S. Pat. Nos. 4,668,586 and 4,695,521 are directed to anodes and to batteries containing the anodes. The anodes comprise a mixture of a conjugated backbone polymer and another electroactive material selected from the group consisting of metals which alloy with alkali metals such as aluminum and lead, and alkali metal cation insertion materials such as transition metal chalcogenides. U.S. Pat. Nos. 4,668,596 and 4,695,521 also describe cathodes comprised of sodium cobalt dioxide. Moreover, L. W. Shacklette and T. R. Jow, "Rechargeable Electrodes From Sodium Cobalt Bronzes", Electrochemical Soc. Abstract No. 64, Honolulu, Oct. 18-23, (1987) and T. R. Jow and L. W. Shacklette, Electrochem. Soc., Abstract No. 67, Honolulu, Oct. 18-23, (1987) "A Rechargeable Cell Based on a Conductive Polymer Alkali-Metal Alloy Composite Electrode" described the use of sodium cobalt dioxide electrodes.